Magadiite is a hydrous sodium silicate mineral (NaSi7O13(OH)3·4(H2O)) which precipitates from alkali brines as an evaporite phase. It forms as soft (Mohs hardness of 2) white powdery monoclinic crystal masses.[3][4] The mineral is unstable and decomposes during diagenesis leaving a distinctive variety of chert (Magadi-type chert).[7]
The mineral was first described by Hans P. Eugster in 1967 for an occurrence in Lake Magadi, Kenya, and is also found at Olduvai Gorge, Tanzania.[4][7] It is also reported from alkalic intrusive syenites as in Mont Saint-Hilaire, Canada.[3]
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